Perpendicular magnetic recording system with medium having thin soft underlayer and recording head having thick-throat trailing shield

Abstract

A perpendicular magnetic recording data storage system combines a perpendicular medium that has a thin low-magnetic-permeability or “soft” underlayer (SUL) with a recording head that has a trailing shield (TS) with a thick throat height, i.e., a thickness in a direction orthogonal to the recording layer of the medium. The SUL is thin enough and has a low enough magnetic permeability to become saturated in a region beneath the trailing gap of the head during writing, but the throat height of the TS is thick enough to prevent the TS from becoming magnetically saturated during writing. The magnetic saturation of the SUL during writing changes the magnetic reluctance such that more of the magnetic flux going through the SUL changes direction (“field undershoot”) and goes to the TS. If the permeability of the SUL is so low (e.g., close to unity) that the SUL does not magnetically saturate, field undershoot may still occur because the reluctance from the SUL to the TS is still smaller than the reluctance from the SUL to the return pole (RP). Field undershoot enables a high write field gradient, which results in narrower magnetic transitions.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates generally to perpendicular magnetic recording data storage systems, and more particularly to a system that uses a medium with a recording layer formed over a “soft” or relatively low-coercivity magnetically permeable underlayer, and a recording head with a single write pole and a trailing shield.[0003]2. Description of the Related Art[0004]Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer, is a promising path toward ultra-high recording densities in data storage systems, such as hard disk drives (HDDs). One type of system uses a recording head with a single write pole (WP) and a “dual-layer” recording disk with the perpendicular magnetic data recording layer (RL) formed over a “soft” or relatively low-coercivity magnetically permeable underlayer (SUL). The SUL serves as a return path for magnetic flux from t...

AI Technical Summary

Benefits of technology

[0007]The perpendicular magnetic recording data storage system of this invention combines a perpendicular medium that has a thin low-magnetic-permeability SUL with a recording head that has a TS with a thick throat height, i.e., a thickness in a direction orthogonal to the recording layer. The SUL is thin enough and has a low enough magnetic permeability to become saturated in a region beneath the trailing gap of the head during writing, but the throat height of the TS is thick enough to prevent the TS from becoming magnetically saturated during writing. The TS may be magnetically connected to the yoke or the RP, or it may be “floating”, i.e., not magnetically connected to either the yoke or the RP. The SUL has a magnetic permeability less than about 25 and a thickness less than about 50 nm. The TS has a magnetic permeability greater than about 100 and a throat height greater than about 40 nm. During writing, a small region at the top of the SUL beneath the trailing gap becomes magnetically saturated, which changes the magnetic reluctance such that more of the magnetic flux going through the SUL changes direction (“field undershoot”) and goes to the TS. If the permeability of the SUL is so low (e.g., close to unity) that the SUL does not magnetically saturate, field undershoot will still occur because the reluctance from the SUL to the TS is still smaller than the reluctance from the SUL to the RP. Field undershoot enables a high write field gradient, which results in narrower magnetic transitions. Narrower magnetic transitions reduce the media “jitter” noise, enabling a higher linear data recording density.

Problems solved by technology

This nearly parallel alignment of the write field with the RL easy axis has the disadvantage that relatively high write fields are necessary to reverse the magnetization in the RL.

It can be difficult and costly to manufacture large numbers of these types of perpendicular magnetic recording HDDs.

The disk requires a relatively thick SUL to avoid magnetic saturation, which requires additional material and increases the manufacturing time and cost.

This will require a recording head with a relatively thin TS with tight tolerances to increase the write field, which makes high-yield manufacturing difficult.

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